Dyes have been included in laundry treatment products for many years. Perhaps the oldest use of dyes is to add a substantive coloured dye to coloured clothes which require rejuvenation of colour for example a substantive blue dye for rejuvenation of denim. These compositions usually contain a relatively high concentration of substantive dye. More recently non-substantive dyes have also been used to colour otherwise white laundry detergent compositions. In the case of particulate detergents this has been in the form of so-called speckles to add colour to an otherwise white powder, however laundry detergent powders which are completely blue are also known. When dyes have been included in laundry treatment products in this way it was regarded as essential that non-substantive dyes were used to prevent undesired staining of washed fabrics.
It is also known that a small amount of blue or violet dye impregnated into an otherwise ‘white’ fabric can appear to have enhanced whiteness as described in Industrial Dyes (K. Hunger ed Wiley-VCH 2003). Modern white fabrics are sold with some dye in their material in order to enhance the whiteness at the point of sale of the garment. This dye is often blue or violet though other colours are used. However once these garments are worn and subsequently washed with a detergent composition the dye is rapidly removed from the fabric often due to dissolution by a surfactant solution. Dye is also lost by reaction with bleach in the wash and fading due to light. This results in a gradual loss of whiteness in addition to any other negative whiteness effects such as soiling. In many cases this leads to the appearance of a yellow colour on the cloth.
Accordingly, the present invention provides a laundry treatment composition according to claim 1.